Tamijuddin Sarker, a senior police officer, said the student was arrested on Saturday night, hours after Rezaul Karim Siddique, a 58-year-old English professor, was hacked to death in the northern city of Rajshahi.

"The student was not formally charged with the murder but was detained for interrogation," the officer said, adding that a six-member panel of investigators had begun working to resolve the murder.

University professor hacked to death in Bangladesh

Siddique was attacked from behind with machetes as he walked to the bus station from his home.

Two or three assailants rode up on a motorcycle and attacked Siddique, slitting his throat and hacking him to death.

On Sunday, Rajshahi University teachers went on strike to demand punishment of the killers, while students staged a demonstration on campus.

They called on the government to arrest the criminals and ensure safety of the teachers, writers and free thinkers.

Al Jazeera's Maher Sattar, reporting from Dhaka, said it was unclear why Siddique was targeted.

"The police say that the manner of his murder was very similar to the others and they believe that it is a religiously motivated attack," he said.

"His colleagues say Siddique had never been publicly critical of Islam, unlike the seven others who have been murdered in the same way.

"He had been a cultural activist, not someone who had been critical of religion, and his cultural activities were seen as unreligious.

"He launched a music school in a very conservative village, so the criteria for targeting people appear to have been broadened."

ISIL claimed that its fighters killed Siddique because "he promoted atheism", according to the Amaq news agency, which is affiliated with the group.